DE 197 48 556 A1 discloses a probe for an eddy current measurement with a ferromagnetic signal amplification, the signal amplification being produced by a rigid ferritic core. With a probe formed by a rigid substrate on which planar coils are mounted, test pieces with a planar surface can be measured. In the case of non-planar surfaces, the probe must be adapted in its shape to a surface of the test piece; otherwise, incorrect measured values are obtained.
A probe with eddy current measurement with ferromagnetic signal amplification for planar test pieces is also known from U.S. Pat. No. 6,002,251.
U.S. Pat. No. 5,389,876 discloses a probe for an eddy current measurement, which however produces only weak signals.